1. Field of Invention
This invention relates generally to medical devices and procedures, and more particularly to a method and system of deploying a stent in a vascular system.
2. Related Art
Prostheses for implantation in blood vessels or other similar organs of the living body are, in general, well known in the medical art. For example, prosthetic vascular grafts formed of biocompatible materials (e.g., Dacron or expanded polytetrafluoroethylene (ePTFE) tubing) have been employed to replace or bypass damaged or occluded natural blood vessels.
A graft tube material supported by a framework is known as a stent-graft or endoluminal graft. In general, the use of stents and stent-grafts for treatment or isolation of vascular aneurysms and vessel walls which have been thinned or thickened by disease (endoluminal repair or exclusion) is well known.
Many stents and stent-grafts are “self-expanding”, i.e., inserted into the vascular system in a compressed or contracted state, and permitted to expand upon removal of a restraint. Self-expanding stents and stent-grafts typically employ a wire or tube configured (e.g., bent or cut) to provide an outward radial force and employ a suitable elastic material such as stainless steel or nitinol (nickel-titanium). Nitinol may additionally employ shape memory properties.
The self-expanding stent or self-expanding stent-graft is typically configured in a tubular shape, sized to have a slightly greater diameter than the diameter of the blood vessel in which the stent or stent-graft is intended to be used. In general, rather than inserting it in a traumatic and invasive manner using open surgery, stents and stent-grafts are typically deployed through a less invasive intraluminal delivery, i.e., cutting through the skin to access a lumen or vasculature or percutaneously via successive dilatation, at a convenient (and less traumatic) entry point, and routing the compressed stent or stent-graft in a delivery system through the lumen to the site where the prosthesis is to be deployed.
Intraluminal deployment in one example is effected using a delivery catheter with coaxial inner tube, sometimes called an inner tube (plunger), and an outer tube, sometimes called the sheath, arranged for relative axial movement. The stent or stent-graft is compressed and disposed within the distal end of the sheath in front of the inner tube.
The catheter is then maneuvered, typically routed though a vessel (e.g., lumen), until the end of the catheter containing the stent or stent-graft is positioned in the vicinity of the intended treatment site. The inner tube is then held stationary while the sheath of the delivery catheter is withdrawn. The inner tube prevents the stent-graft from moving back as the sheath is withdrawn.
As the sheath is withdrawn, the stent or stent-graft is gradually exposed from its proximal end to its distal end. The exposed portion of the stent or stent-graft radially expands so that at least a portion of the expanded portion is in substantially conforming surface contact with a portion of the interior of the blood vessel wall.
The proximal end of the stent or stent-graft is the end closest to the heart by way of blood flow path whereas the distal end of the stent or stent-graft is the end furthest away from the heart during deployment. In contrast and of note, the distal end of the catheter is usually identified to the end that is farthest from the operator (handle) while the proximal end of the catheter is the end nearest the operator (handle).
For purposes of clarity of discussion, as used herein, the distal end of the catheter is the end that is farthest from the operator (the end furthest from the handle) while the distal end of the stent-graft is the end nearest the operator (the end nearest the handle or the handle itself), i.e., the distal end of the catheter and the proximal end of the stent-graft are the ends furthest from the handle while the proximal end of the catheter and the distal end of the stent-graft are the ends nearest the handle. However, those of skill in the art will understand that depending upon the access location, the distal and proximal end descriptors for the stent-graft and delivery system description may be consistent or opposite in actual usage.
Some self-expanding stent deployment systems and stent-graft deployment systems are configured to have each exposed increment of the stent or stent graft at the proximal end of the stent-graft deploy (flare out or mushroom) as the sheath is pulled back. The proximal end of the stent-graft is typically designed to expand to fixate and seal the stent-graft to the wall of the vessel during deployment. Such a configuration leaves little room for error in placement since re-positioning the stent-graft after initial deployment, except for a minimal pull down retraction, is difficult, if possible at all. The need to achieve accurate proximal end positioning of the stent-graft first makes accurate pre-deployment positioning of the stent or stent-graft critical.